Three monoclonal antibodies (IgG₂) have been produced from hybridomas obtained by fusion of murine myeloma cells and spleen cells of mice hyperimmunized with gamma‐interferon‐treated neuroblastoma cells. The 3 MAbs, 7A4, 2A6 and IG8, detected an antigen present on neuroblastoma tumors and cell lines, but also on some neuro‐ectoderm‐derived tissues and cells. All 3 clones were shown to react with an epitope of the di‐sialo‐ganglioside GD2 molecules highly expressed by some neuro‐ectoderm‐derived tumors, mainly neuroblastoma. Whereas MAb IG8 specificity was restricted to GD2 and its o‐acylated form, MAb 2A6 and 7A4 were also able to detect GD3 at high concentration of antibody as shown by TLC analysis and immunodetection. The 3 MAbs were able to lyse 100% neuroblastoma cells in the presence of rabbit or human complement. Direct binding assays with ¹²⁵‐labelled MAbs showed that MAb 7A4 might be a good candidate for in vivo immunolocalization experiments. The high proportion of anti‐GD2 MAbs obtained by our fusion and the increased binding of anti‐GD2 MAbs on gamma‐IFN‐treated neuroblastoma cells suggests a modulation of the exposure and an increase in the immunogenicity of GD2 induced by gamma‐IFN.